Switching regulators are designed to provide a regulated output voltage from an unregulated input voltage. They are frequently implemented in battery-powered electronic devices to regulate the battery output voltage which, when charged or discharged, can be greater than, less than, or substantially the same as the desired output voltage.
In general, a switching regulator works by periodically transferring small amounts of energy from the input voltage source to the output. This is accomplished with the help of one or more power switches and a controller that regulates the rate at which energy is transferred to the output. For example, a duty cycle controller can be used to generate a duty signal that instructs the switches when to toggle on and off.
There are several different topologies for implementing a duty cycle controller. Depending on the topology, the ratio of the on time of switch to the switching period can be altered in a number of ways. Two common approaches are pulse-width modulation (PWM) and variable frequency control topologies. In PWM-based control topologies, the switching period is fixed, and the on time of the switch is varied. Conversely, in variable frequency control topologies, the switching period is not fixed but rather changes as the on time and/or off time of the switch is varied.
Hysteretic switching regulators are one type of switching regulator based on a variable frequency control topology. These switching regulators have several advantages over switching regulators based on PWM control topologies. For example, unlike switching regulators based on PWM control topologies, hysteretic switching regulators do not require an oscillator and therefore are generally simpler to implement.
However, the potentially wide switching frequency variation of hysteretic switching regulators during operation makes it difficult and expensive to filter electromagnetic interference (EMI) caused by switching, which can interfere with sensitive RF components near and powered by the regulator.
Therefore, what is needed is a hysteretic switching regulator with reduced EMI.
Features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number. It should be understood that the drawings, and elements therein, are not necessarily drawn to scale.